The present invention relates to a vacuum cartridge in particular for an electrical protection apparatus such as a switch or circuit breaker, said cartridge comprising an enclosure of appreciably cylindrical shape closed by two end-plates, two arcing contacts extending axially inside the enclosure, at least one of which contacts called the movable contact is connected to an operating mechanism and is slidingly mounted between a closed position of the contacts corresponding to a rest position of the apparatus and a position in which the arcing contacts are separated and form an electric arc between them, separation of the contacts resulting in breaking of the electrical circuit, and a means for producing an axial magnetic field for diffusion of the arc in the arc formation area.
A cartridge of this kind is described for example in the documents FR 2,682,808 or FR 2,726,396.
The present invention is based on the following new observations. The behavior of the electric arc is such that in spite of the presence of large axial magnetic fields, the arc is all the more concentrated the greater the current intensity. The diffused arc, covering the whole surface of the contacts when breaking takes place with a weak current, is transformed into an arc in the form of a column, which arc heats a small part (10%) of the arcing contact surface intensely.
This electric arc, due to the high concentration of its intensity, causes melting of the contact material at the foot of the arc. The resulting liquid spreads over the whole of the contact surfaces. Thus, the liquid distributes the arcing energy above the contacts. This causes cooling of the arc in two stages. Firstly, the arc heats the contact material until the latter melts, then the liquid flows out of the arcing area. Solutions have been proposed to distribute the arcing energy better so as to increase the breaking capacity. All these solutions act directly on the arc, for example enlarging the surface of the arc, subdividing the arc or making the arc move.
Cartridges are moreover also known wherein the contacts are provided with slits. These slits are designed to reduce the induced currents in case of an axial magnetic field being used, or to create either a radial or an axial magnetic field.
The object of the present invention is to improve the breaking capacity of cartridges of this kind without exerting any manipulation on the arc.
For this purpose, the object of the present invention is to achieve a vacuum cartridge of the previously mentioned kind, this cartridge being characterized in that it comprises means, called first means, to speed up cooling especially of the contact material in liquid form flowing on the contact surface of the contact or contacts during breaking, said liquid coming from melting of the contact material due to the concentration effect of the arc during breaking.
According to a particular embodiment of the invention, these first means comprise means, called second means, for increasing the contact surface between the contact(s) and the above-mentioned liquid so as to create surfaces hidden for the arc but accessible for the liquid.
According to a particular embodiment, these means comprise at least one slit made in one or each of the contacts and arranged in such a way as to receive the above-mentioned liquid and facilitate flow thereof.
Thus, in this embodiment, the slits are arranged to receive the liquid, unlike known cartridges of the prior art comprising slits in the contacts. In the latter cartridges, the contact liquid, due to its capillarity and to the arrangement of these slits, does not in fact flow inside the slits.
According to another particular embodiment, these second means comprise at least one groove designed to receive the above-mentioned liquid and extending radially inside the contact(s), from close to the central part of the contact(s) up to its (their) periphery.
According to another embodiment, these second means comprise at least one orifice made in one or each of the contacts, said orifice(s) joining the upper face and the lower face of the (or each) contact and presenting a diameter smaller than the diameter of the electric arc.
According to another feature, these first means comprise means called third means for increasing the speed of flow of the liquid.
Advantageously, these first means comprise second means and third means, the second means comprising slits and, according to the third means, the angle formed between the direction of the initial flow of the liquid and the inlet direction of the liquid into the slits is smaller than or equal to 90xc2x0.
According to another feature, according to these second means, one or each of the arcing contacts is hollow and comprises an orifice in its contact surface giving access to the opposite surface of the contact(s), which opposite surface thus takes part in cooling, supply of the contact(s) being performed via the periphery of the contact(s).
According to a particular feature, the edge(s) of the contact(s) is (are) cut in such a way as to form a coil designed to create the above-mentioned axial magnetic field for diffusion of the arc.
According to another particular feature, the axial magnetic diffusion field created is a multipole field and one or each of the contacts comprises as many orifices as poles.